In the processing of tomato-based products, such as tomato juice, tomato paste, catsup, and the like, the product consistency is dependent upon the presence of pectic substances. The freshly cut or crushed tomato fruit must be quickly heated to above 180.degree. F. (82.degree. C.) in order to inactivate pectin enzymes naturally present in the fruit. If temperatures lower than this are employed, the breakdown of pectic substances by the enzymes will result in product of low consistency, that is, thin and watery products.
Upon maceration of tomatoes, the enzyme pectinmethylesterase rapidly demethylates the pectic substances naturally present in tomatoes producing pectic and pectinic acids. These acids are then depolymerized by polygalacturonase. The enzyme polygalacturonase (also known as pectinase or pectic acid depolymerase) rapidly depolymerizes pectic and pectinic acids into smaller polygalacturonic acids and finally into D-galacturonic acid and galacturonic acid methyl ester. The resulting lack of pectic substances is responsible for a loss of colloidal properties and for poor consistency of the product. Heating the tomato macerate to above 180.degree. F. (82.degree. C.) deactivates these pectin enzymes. Since polygalacturonase does not break down highly methylated pectins, it is dependent upon pectin-methylesterase to provide pectin acid substrate. Deactivation of pectin-methylesterase therefore blocks action by polygalacturonase and indirectly prevents breakdown of pectic substances in tomato products during processing. It is common industry practice to process fresh tomatoes initially at a temperature of at least about 180.degree. F. (82.degree. C.) to deactivate the pectin enzymes and prevent breakdown of pectic substances. A formulated tomato product is often packed in a separate processing operation later in time using the deactivated tomato macerate as an ingredient. However, this operation is also commonly conducted at high temperatures of at least about 180.degree. F. (82.degree. C.) or more in order to sterilize the product. High temperature processing can lead to loss in flavor. See U.S. Pat. No. 3,549,384 of Walker et al., issued Dec. 22, 1970; and McColloch, R. J., et al., Food Technology, Vol. 3, pp. 94-96 (1949), and Vol. 4, pp. 339-343 (1950).
In contrast to enzyme reactions causing thin product consistency in the processing of fresh tomatoes, enzyme reactions promote firming of product in the processing of some fruits and vegetables. The enzyme, pectin methylesterase, is activated during low-temperature blanching at 158.degree.-180.degree. F. (70.degree.-82.degree. C.), and inactivated during high-temperature blanching at 190.degree.-212.degree. F. (88.degree.-100.degree. C.) Pectin methylesterase hydrolyzes esterified methanol (sometimes referred to as methoxyl groups) from carboxyl groups on pectin to yield pectinic and pectic acids. Pectin lacks substantial numbers of free carboxyl groups, rendering it water soluble and free to migrate from the cell wall. Pectinic acid and pectic acid possess large numbers of free carboxyl groups and they are relatively insoluble, especially in the presence of calcium ions. As a result, in the absence of the active enzyme polygalacturonase they remain in the cell wall during processing and produce firm textures. Firming effects through activation of pectin methylesterase have been observed for snap beans, potatoes, cauliflower, and sour cherries. These effects occur for products which do not contain active polygalacturonase and which are packed substantially whole as opposed to the macerated tomatoes used in the preparation of juices, sauces, and the like of the present invention. Addition of calcium ions in conjunction with enzyme activation leads to additive firming effects. SeePrinciples of Food Science, Part I--Food Chemistry, O. R. Fennema, Ed., Marcel Dekker Inc., New York, N.Y. p. 482 (1976).
Excessive thermal processing of tomato products can lead to loss in flavor acceptability due to the development in the product of burned and browned flavors, as well as other thermal reaction off flavors. Acidification of such products to a pH of 4.6 or below renders them microbiologically safe if the products are sealed into containers at elevated temperatures, and held for sufficient time to destroy microorganisms prior to cooling. Sognefest et al., Food Technology, Vol. 1, p. 78 (1947), describe a method of canning tomato juice and tomato juice cocktail at a pH below 4.5 which employs high-temperature-short-time processing in a heat exchanger prior to filling in cans. Decreasing the processing time at which the product is maintained at elevated temperatures reduces loss of valuable flavor components.
When preparing tomato products from ingredients such as tomato paste, crushed tomatoes, and the like, which are substantially free of active enzymes due to previous processing, it is desirable to employ low processing temperatures followed by a high-temperature-short-term sterilization in order to minimize flavor loss by minimizing the cumulative time the product is maintained at elevated temperatures. It has now been determined that when a tomato product made from tomato paste or similar ingredients substantially free of active enzymes due to previous processing is combined with one or more members of the Allium botanical genus, in particular, onion, garlic, or a mixture thereof, and processed at a temperature range below about 160.degree. F. (71.degree. C.) to reduce loss of flavor, a thick gel is formed throughout the product upon cooling. The tomato product without added onion or garlic when subjected to the same processing conditions results in product of normal consistency. It is unexpected that allium causes gel formation in tomato products. The prevalent practice of quickly raising the process temperature to above 180.degree. F. (82.degree. C.) explains why gel formation in tomato products due to onion and garlic has not been noted in commercial practice. Even if the allium were added when the tomato product is below about 160.degree. F. (71.degree. C.), the temperature is raised so quickly that gel formation does not occur.
The occurrence of the gels during low temperature processing of tomato products containing allium suggests that pectin enzymes are present in onion and garlic. The prior art teaches product firming is promoted for some fruits and vegetables, packed substantially whole, in the temperature range of 160.degree. F. (71.degree. C.) to 180.degree. F. (82.degree. C.) due to activation of pectin methylesterase. It has now been determined, however, that for tomato products processed at a temperature range of from about 160.degree. F. (71.degree. C.) to 180.degree. F. (82.degree. C.), with or without added onion or garlic, thick gelling not occur. It is unexpected that gel formation in tomato products containing allium can be prevented by processing in this temperature range which is associated with promoting product firming.
"Normal consistency" is used herein to mean that consistency obtained by current commercial practices wherein the tomato pectin enzymes have been deactivated by heating. "Tomato product" is used herein to mean a product containing tomatoes wherein the tomato pectin enzymes have been deactivated by heating when freshly cut or crushed.
Thick gelling or firming of a tomato product, such as a juice or sauce, can render the product unacceptable to consumers despite better flavor due to the low temperature processing. However, the gelling can be advantageous to a product wherein enhancement of its colloidal properties is desirable. Previous known methods for controlling tomato product consistency involve adding or eliminating water to change the level of tomato solids present. The process of the present invention is advantageous in that product consistency can be controlled without altering the level of tomato solids in the product. Enhancement of product consistency without increasing the level of tomato solids could be an economical means of improving the texture of some products. A method for processing tomato-based products containing onion, garlic, or a mixture thereof, primarily at a low temperature range to prevent loss of flavor, wherein the product consistency can be optimized, is desirable.
Accordingly, it is an object of this invention to provide a method for minimizing flavor loss and controlling the consistency of a tomato product processed primarily at temperatures below the current commercial practice of 180.degree. F. (82.degree. C.) and above prior to sterilization when allium, in particular, onion, garlic, or a mixture thereof, is present.
It is a further object of this invention to provide a method for deactivating the gel-inducing properties of allium in the presence of tomato products.
It is a further object of this invention to provide a method for enhancing the colloidal properties of a tomato product through use of allium without increasing the level of tomato solids present in the product.
These and other objects of the invention will be evident from the following disclosure. All percentages are by weight unless otherwise indicated.